(1) Field of the Invention
The present invention pertains to a battery operated grease gun and in particular to a pump mechanism of the grease gun that employs a speed reducing and torque increasing transmission that rotates a final driver that is a part of the transmission, and a sliding yoke that is reciprocated by the final driver and is coupled to a plunger that dispenses the grease under pressure where the plunger is mounted to the yoke for relative movement therebetween.
(2) Description of the Related Art
A conventional hand operated grease gun is basically comprised of a housing containing a pump mechanism comprised of a plunger that reciprocates in a tubular pump chamber, a check valve and discharge spout that communicate with the pump chamber, a grease reservoir that communicate with the pump chamber tube and is adapted to have a tubular body containing grease or a grease reservoir attached thereto, and a manually manipulated pump lever or handle that is pivotally connected to the housing and is connected to the pump plunger to reciprocate the plunger in the pump chamber on manual pivoting movement of the lever. In manually operated grease guns of this type, the rate at which the lever is manually pivoted determines the rate at which grease is dispensed through the discharge spout. In addition, the manual force exerted on the lever multiplied by the length of the lever used as leverage determines the force or pressure of the grease dispensed from the gun through the discharge spout.
More recent designs in grease guns have resulted in battery operated grease guns that eliminate the need to manually pivot the grease gun lever. This is accomplished by providing an electric motor that reciprocates the pump plunger to dispense grease under pressure from the battery operated grease gun. Many of the features of the manually operated grease gun are employed in the battery operated grease gun. Examples of battery operated grease guns and similar extruders are disclosed in the U.S. patents of Wegmann et al. U.S. Pat. No. 4,257,540, issued Mar. 24, 1981; Barry U.S. Pat. No. 5,404,967, issued Apr. 11, 1995; Shih et al. U.S. Pat. No. 5,609,274, issued Mar. 11, 1997; and Barry U.S. Pat. No. 5,685,462, issued Nov. 11, 1997.
In many battery operated grease guns the rotation of an electric motor output shaft is transformed into linear reciprocating movement of the grease gun plunger which dispenses grease under pressure from the grease gun. There are many different types of mechanisms and gearing transmissions employed in the prior art that convert the rotating output of the electric motor output shaft to the linear reciprocating movement of the plunger. A drawback observed in the transmission of rotary movement to linear reciprocating movement is that the plunger, in addition to being subjected to forces directed along the line of its linear reciprocation will also be subjected to forces that are not directed along the line of linear reciprocation due to the plunger being driven from the rotating output shaft of the electric motor. With the plunger being confined to reciprocating in a pump chamber that is basically a cylindrical tube, the forces directed off line with the line of plunger reciprocation can have a tendency to cause the plunger to bind or catch in the pump chamber as the plunger reciprocates. This can affect the dispensing performance of the battery operated grease gun and can lead to wear of the plunger and pump chamber wall which could lead to the complete inability of the battery operated grease gun to dispense grease under pressure.
In addition, because it is often necessary that the battery operated grease gun dispense grease under a significant pressure in order for it to perform satisfactorily, a significant force must be exerted on the plunger as it dispenses grease from the grease gun. The significant force is generated by a gearing transmission or similar mechanism that reduces the output speed of rotation of the electric motor and increases its torque. Such power transmission mechanisms often cannot be constructed compactly and many prior art battery operated grease guns have been designed that are awkward and difficult to use due to the size requirements of their power transmissions and the positioning of the power transmission, battery and electric motor on the grease gun.
A battery operated grease gun having a compact power transmission design that also eliminates the potential of the plunger binding or catching in the pump chamber as it reciprocates would overcome the disadvantages experienced in many prior art battery operated grease gun designs.